As early as 1985, the author recalls re-occurring discussions of the effects of puncture holes from component leads and stapling of static shielding bags.

In July 2013, the ESD Experts page on LinkedIn® started a discussion by a USA computer manufacturing company that generated participation from end users, suppliers and consultants both here and abroad. In years past, some held opinions that pin holes do not greatly affect static shielding of metallized bags. There is, however, minimal published data to fall back upon regarding this subject matter.

One major factor influencing Type III (Mil-PRF-81705E) or a Level 3 (ANSI/ESD S11.4) ESD shielding bag constitutes fracturing of its thin metallized vacuum deposited layer. Excessive wear and pin holes from leads of circuit cards pose risks. The size and magnitude of the pin holes determine bag attenuation from a high voltage discharge. In Figure 1, left, the reader will observe through hole (“thru-hole”) components and a single microscopic puncture to the right.

This article specifically illustrates the differences in shielding bag performance due to pin holes and stapling. Conditioning took place at 12.3%RH, 73.4°F for 48 hours. Note: ANSI/ESD STM11.31 testing is conducted at 12% & 50%RH after 48 hours of preconditioning for qualification.

In Figure 3, left, one can observe a staple affixed to a shielding bag; the photograph to the right represents 3 puncture holes in another ESD bag. Each bag was subjected to six (6) discharges at 1KV. A new bag free from pin holes, staples or blemishes produced a series of waveforms as illustrated in Figure 4 and Table 1.

Figure 3

Figure 4

PeakCurrent (492mA) 367

12%RH 1

Bag 1

mA

HVD

Bag 1

nJ

HVD

1

38.00

1000v

1

13.03

1000v

2

38.00

1000v

2

13.14

1000v

3

38.40

1000v

3

13.12

1000v

4

38.00

1000v

4

13.16

1000v

5

38.00

1000v

5

13.12

1000v

6

38.00

1000v

6

13.10

1000v

Average

38.07

No Holes

Average

13.11

No Holes

Median

38.00

Median

13.12

Minimum

38.00

Minimum

13.03

Maximum

38.40

Maximum

13.16

St. Dev.

0.16

St. Dev.

0.04

PeakCurrent (504mA) 2

12%RH 2

Bag 2

mA

HVD

Bag 2

nJ

HVD

1

43.20

1000v

1

17.72

1000v

2

42.40

1000v

2

17.53

1000v

3

42.40

1000v

3

17.30

1000v

4

42.40

1000v

4

17.38

1000v

5

42.40

1000v

5

17.39

1000v

6

42.40

1000v

6

17.26

1000v

Average

42.53

1 Hole

Average

17.43

1 Hole

Median

42.40

Median

17.39

Minimum

42.40

Minimum

17.26

Maximum

43.20

Maximum

17.72

St. Dev.

0.33

St. Dev.

0.17

PeakCurrent (492mA) 4

12%RH 4

Bag 3

mA

HVD

Bag 3

nJ

HVD

1

48.00

1000v

1

23.00

1000v

2

48.00

1000v

2

22.66

1000v

3

48.00

1000v

3

21.97

1000v

4

48.00

1000v

4

22.51

1000v

5

48.00

1000v

5

22.05

1000v

6

48.00

1000v

6

21.86

1000v

Average

48.00

Stapled

Average

22.34

Stapled

Median

48.00

Median

22.28

Minimum

48.00

Minimum

21.86

Maximum

48.00

Maximum

23.00

St. Dev.

0.00

St. Dev.

0.45

PeakCurrent (504mA)

12%RH 5

Bag 4

mA

HVD

Bag 4

nJ

HVD

1

44.80

1000v

1

21.31

1000v

2

46.40

1000v

2

21.42

1000v

3

46.40

1000v

3

21.20

1000v

4

44.80

1000v

4

21.14

1000v

5

46.40

1000v

5

21.07

1000v

6

44.80

1000v

6

21.08

1000v

Average

45.60

2 Holes

Average

21.20

2 Holes

Median

45.60

Median

21.17

Minimum

44.80

Minimum

21.07

Maximum

46.40

Maximum

21.42

St. Dev.

0.88

St. Dev.

0.14

PeakCurrent (504mA)

12%RH 6

Bag 1

mA

HVD

Bag 1

nJ

HVD

1

45.20

1000v

1

19.99

1000v

2

44.80

1000v

2

19.98

1000v

3

45.20

1000v

3

19.92

1000v

4

45.20

1000v

4

19.95

1000v

5

44.00

1000v

5

19.77

1000v

6

44.40

1000v

6

19.90

1000v

Average

44.80

3 Holes

Average

19.92

3 Holes

Median

45.00

Median

19.94

Minimum

44.00

Minimum

19.77

Maximum

45.20

Maximum

19.99

St. Dev.

0.51

St. Dev.

0.08

PeakCurrent (496mA) 368

12%RH 1

Bag 1

mA

HVD

Bag 1

nJ

HVD

1

50.40

1000v

1

25.10

1000v

2

50.80

1000v

2

25.17

1000v

3

50.00

1000v

3

25.06

1000v

4

50.40

1000v

4

24.97

1000v

5

50.40

1000v

5

24.97

1000v

6

50.80

1000v

6

25.16

1000v

Average

50.47

4 Holes

Average

25.07

4 Holes

Median

50.40

Median

25.08

Minimum

50.00

Minimum

24.97

Maximum

50.80

Maximum

25.17

St. Dev.

0.30

St. Dev.

0.09

PeakCurrent (496mA) 2

12%RH 2

Bag 2

mA

HVD

Bag 2

nJ

HVD

1

48.00

1000v

1

23.99

1000v

2

48.00

1000v

2

24.05

1000v

3

48.00

1000v

3

23.77

1000v

4

47.20

1000v

4

23.79

1000v

5

47.60

1000v

5

23.91

1000v

6

47.60

1000v

6

23.84

1000v

Average

47.73

5 Holes

Average

23.89

5 Holes

Median

47.80

Median

23.88

Minimum

47.20

Minimum

23.77

Maximum

48.00

Maximum

24.05

St. Dev.

0.33

St. Dev.

0.11

PeakCurrent (496mA) 3

12%RH 3

Bag 3

mA

HVD

Bag 3

nJ

HVD

1

47.60

1000v

1

22.98

1000v

2

47.20

1000v

2

23.06

1000v

3

47.20

1000v

3

23.08

1000v

4

48.00

1000v

4

23.04

1000v

5

47.60

1000v

5

22.99

1000v

6

47.60

1000v

6

22.92

1000v

Average

47.53

6 Holes

Average

23.01

6 Holes

Median

47.60

Median

23.02

Minimum

47.20

Minimum

22.92

Maximum

48.00

Maximum

23.08

St. Dev.

0.30

St. Dev.

0.06

PeakCurrent (496mA) 4

12%RH 4

Bag 3

mA

HVD

Bag 3

nJ

HVD

1

52.00

1000v

1

28.39

1000v

2

52.80

1000v

2

28.36

1000v

3

52.00

1000v

3

28.11

1000v

4

52.40

1000v

4

28.19

1000v

5

52.40

1000v

5

28.43

1000v

6

52.00

1000v

6

28.03

1000v

Average

52.27

20 Holes

Average

28.25

20 Holes

Median

52.20

Median

28.27

Minimum

52.00

Minimum

28.03

Maximum

52.80

Maximum

28.43

St. Dev.

0.33

St. Dev.

0.17

Table 1: 12.3%RH, 73.4°F after 48 hours

Initial testing of a brand new electrostatic discharge shielding bag (Type III) measured 13nj which is under the limit (<20nJ) set by ANSI/ESD S11.4. However, these shielding results still fall short of the Mil-PRF-81705E requirement of 10nJ max.

A single staple did impact a new bag’s shielding performance from approximately 13nJ to 19nJ (Figure 5). Additional staples would pose a greater problem. In like manner, 20 pin holes were created by pushing an ESD device through a new bag (Figure 6) leading to results in excess of <20nJ. This finding is significant since pin holes caused the bag to fail at 28nJ. The findings for each bag can be viewed in Table 2. The size of the holes did vary from bag to bag.

Figure 5Figure 6Table 2 (click image for larger view)

In summary, it is clearly evident by conducting the ANSI/ESD STM11.31 testing for electrostatic discharge attenuation that ESD bags with pin holes pose risks both inside and outside of an ESD Protected Area (EPA). Reliance upon data avoids speculation and warrants further study by the Author on ESD bag longevity in a manufacturing and distribution environment. Other risks include pin holes that will allow moisture pick up to take place, insects to enter, dust to infiltrate a package to compromise cleanliness in addition to contamination of the printed circuit board.